Chemistry Past Questions | West African Examinations Council (WAEC)

Question 1

The minimum amount of energy required for effective collisions between reacting particles is known as

Options

A) Activation energy

B) Bond energy

C) Kinetic energy

D) Potential energy

The correct answer is A.

Explanation:

When reactant particles collide, they must posses a minimum amount of energy for effective collisions to take place. This minimum energy is called activation energy, and it is the energy possessed by reactant particles for products to be formed.

Question 2

The bond formed between ${\text{H}}_2\text{O}$

and ${\text{H}}^{+}$ to form the hydroxonium ${\text{H}}_3{\text{O}}^{+}$

is

Options

A) Dative

B) Covalent

C) Electrovalent

D) Ionic

The correct answer is A.

Question 3

An element $\text{X}$

forms the following oxides ${\text{X}}_2\text{O},\text{XO}$ and ${\text{XO}}_2.$

This phenomenon illustrates the law of ________.

Options

A) Conservation of mass

B) Definite proportion

C) Mass action

D) Multiple proportion

The correct answer is D.

Explanation:

The law of multiple proportions states that when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small, whole numbers.

Question 4

How many moles of oxygen would contain $1.204\times {10}^{24}$

molecules?
NB: Avogadro's constant (NA) $=6.02\times {10}^{23}$

Options

A) 1

B) 2

C) 3

D) 4

The correct answer is B.

Explanation:

$6.02\times {10}^{23}$

molecules is $1$ mole
$1.204\times {10}^{24}$ molecules will be:
$\frac{1.204\times {10}^{2}4\times 1}{6.02\times {10}^{2}3}$
$\frac{1.204\times 10}{6.02}$$=\frac{12.04}{6.02}=2$

moles

Question 5

Which of the following statements about solids is correct?

Options

A) Solid particles are less orderly than those of a liquid

B) Solid have lower densities than liquids

C) Solid particles have greater kinetic energies than those of liquids

D) Solid particles cannot be easily compressed

The correct answer is D.

Explanation:

This is because the molecules of a solid are arranged are so therefore they happen to be closely packed making it hard to compress.

Question 6

Which of the following apparatus can be used to measure a specific volume of a liquid accurately?

Options

A) Beaker

B) Conical flask

C) Measuring cyclinder

D) Pipette

The correct answer is D.

Explanation:

On a pipette there is a line that is particularly designated for measuring a particular amount of liquid (usually 20-25 cm${}^3$

)

Question 7

The general gas equation $\frac{\text{PV}}{\text{T}}=\text{K}$

is a combination of

Options

A) Boyle's and Charles' laws

B) Boyle's and Graham's laws

C) Charles' and Graham's laws

D) Dalton's and Graham's laws

The correct answer is A.

Explanation:

Pvt=K is a combination of Boyle and charles law,Pressure,volume and temperature

Question 8

The spreading of the scent of a flower in a garden is an example of ________.

Options

A) Brownian motion

B) Diffusion

C) Osmosis

D) Tynadal effect

The correct answer is B.

Explanation:

From the definition of diffusion the scent of the flower was able to spread evenly.

Question 9

Propane and carbon (IV) oxide diffuse at the same rate because [H = 1.00, C = 12.0, O = 16.0]

Options

A) They are both gases

B) Their molecules contain carbon

C) They have the same relative molecular mass

D) Both are denser than air

The correct answer is C.

Question 10

The energy which accompanies the addition of an electron to an isolated gaseous atom is

Options

A) Atomization

B) Electronegativity

C) Electron affinity

D) Ionization

The correct answer is C.

Explanation:

Electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.

Explanation provided by Collins Fame

Question 11

An aqueous solution of (NH₄)₂ SO₄ is

Options

A) Acidic

B) Alkaline

C) Amphoteric

D) Neutral

The correct answer is A.

Explanation:

A salt is an ionic compound which is made up of two groups of oppositely charged ions. The overall compound of a salt compound must have an overall electrical charge of 0. Ammonium sulfate, $({\text{NH}}_4{)}_2{\text{SO}}_4$

, can be made by the reaction of ammonia, ${\text{NH}}_3$ with sulfuric acid, ${\text{H}}_2{\text{SO}}_4$

.

Ammonium sulfate $\left(N{H}_4{)}_{2}S{O}_4\right)$

, also called diazanium sulfate, diammonium sulfate and sulfuric acid, diammonium salt, is an inorganic salt that appears as an odorless white solid at room temperature. As the salt of sulfuric acid, a strong acid, and ammonia, a weak base, it forms an acidic solution when added to water.

Question 12

When NH₄Cl_(s) is dissolved in water, the container feels cold to touch. This implies

Options

A) The process is endothermic

B) The process is exothermic

C) NH₄Cl forms a saturated solution

D) NH₄Cl is highly soluble in water

The correct answer is A.

Explanation:

Endothermic reaction will be cold since it absorbs energy from the environment (endothermic will be hot temperature)

Question 13

The pH of four solutions M, N, Q and R are 2, 6, 8 and 11 respectively.
Which of the following deductions about the solutions is correct?

Options

A) The pH of N is increased when the solution is diluted

B) The pH of Q is increased when the solution is evaporated

C) M is the most alkaline solution

D) R is the most acidic solution

The correct answer is A.

Question 14

Consider the following reaction equation
H₃O⁺_(aq) + OH_(aq) → 2H₂O_(l)
The reaction represents

Options

A) Esterification

B) Hydrolysis

C) Neutralization

D) Redox

The correct answer is C.

Explanation:

Neutralization reaction is the reaction between acid and base to produce salt and WATER

Question 15

The refreshing characteristic taste of fizzy drinks is due to the presence of

Options

A) Carbon (IV) oxide

B) Glucose

C) Hydrogen

D) Sodium Citrate

The correct answer is A.

Explanation:

Carbon (IV) oxide or carbon dioxide is a colorless, odorless, incombustible gas, CO${}_2$

, that is formed during respiration, combustion, and organic decomposition, is an essential component in photosynthesis, and is used in food refrigeration, carbonated beverages, inert atmospheres, fire extinguishers, and aerosols.

Question 16

Chemical equilibrium is attained when

Options

A) All the reactants have been completely used up

B) The reaction goes to completion

C) The concentration of reactants and products remain constant

D) The concentration of reactants and products are equal

The correct answer is C.

Question 17

Which of the following factors will affect the rate of the reaction represented by the following equation?

2HCl_(aq) + CaCO_3(s) → CaCl_2(aq) + H₂O_(l) + CO_2(g)

I. Pressure

II. Concentration

III. Nature of reactants

IV. Temperature

Options

A) I and II only

B) II, III and IV only

C) I, II and III only

D) I, II, III and IV

The correct answer is B.

Explanation:

Pressure is out because it only affects gaseous reactant.

Question 18

On evaporation to dryness, 350cm${}^3$

of saturated solution of salt Z gave 55.5g of salt. What is the solubility of the salt? [Z = 101]

Options

A) 1.57 moldm^-3

B) 3.14 moldm^-3

C) 6.28 moldm^-3

D) 12.56 moldm^-3

The correct answer is A.

Explanation:

Saturated solution = 350cm${}^3$

mass of salt Z in saturated solution = 55.5g
Number of moles of salt = $\frac{55.5}{101}$ = 0.55 mole
3503 of solution contains 0.55 mole
1000cm³ will contain $\frac{1000\times 0.55}{350}$

= 1.57 mol/dm³

Question 19

Which of the following salts when dissolved in water will form a solution that will change blue litmus to red?

Options

A) CH₃COONa

B) NH₄Cl

C) NaCl

D) KCl

The correct answer is B.

Explanation:

When $N{H}_{4}Cl$

is dissolved in water, it hydrolyzes to give HCl and $N{H}_{4}OH$. HCl is a strong acid and as such turns blue litmus paper red.
The equation is given below:
$N{H}_4+H_{2}O\to N{H}_{4}Cl+H_{2}O$

Question 20

Which of the following bonds are broken when ethanol is boiled?

I. Covalent bonds

II. Ionic bonds

III. Hydrogen bonds

Options

A) I only

B) II only

C) III only

D) I, II, III

The correct answer is C.

Explanation:

Ethanol is kept as a liquid by hydrogen bonds which hold its molecules close together. Boiling causes the molecules to vibrate faster thereby destroying the bond force. The molecules now held together by no force are set lose and hence evaporate.

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